The research is designed to test hypothesis that activity in the sympathetic division of the nervous system acts to modulate pain perception by efferent control of receptor sensitivity. The first part o the study focuses on identified cutaneous receptors in the cat. Responses to repeated mechanical and /or thermal stimuli are recorded in the presence and absence of conditioning sympathetic stimulation. The second phase of the study will involve recording from spinal second-order sensory neurons and testing for changes in their responses to cutaneous stimulation subsequent to sympathetic stimulation.